I have found a bug in the past in Safari 2.0, and I just found it again. If you go to this website and hover over the "Listen Now!" text near the top, a menu will extend. But if you go to hover over any item in the list that overlaps the Google ad, the menu disappears. The same goes for "Community", "Services". Experiment. You will find that no matter what you try to do, you will not be able to select anything from the menu as long as the Google ad is behind the menu, I think.

I have tried this in Firefox, and everything works great in there.

I reported it to Apple, in there handy little their "Report Bugs to Apple" feature. Just thought that I would give you guys the heads up, if you ever experience it.